In recent years, various techniques are disclosed for easily locating a button in a switch operation screen displayed on a touch sensitive panel of a display unit. For example, Japanese patent document JP-A-H07-319623 discloses a touch panel that has a transparent sheet disposed thereon with a protrusion for indicating a button position. Further, Japanese patent document JP-A-H10-269012 discloses an apparatus including a touch panel for sensing a touching finger of a user in combination with a display unit for displaying a switch operation screen with a superposed outline of a touching finger image. The outline image of the touching finger is derived from imaging the touching finger actually touching the separately positioned touch panel for providing a no-lookaway operability of the switch operation screen on the touch panel.
The disclosure in Japanese patent document JP-A-H07-319623 improves user operability for indicating the button position in the switch operation screen by having the transparent sheet on the touch panel. However, when menus in the switch operation screen is hierarchically structured and variably arranged for controlling, for example, a navigation system, having plural transparent sheets for accommodating respective menus is difficult.
Further, the disclosure in Japanese patent document JP-A-H10-269012 not only requires the protrusion on the surface of the touch panel, but also requires an associated operation of the touch panel and the switch operation screen due to its separate positioning of the display unit away from the touch panel. In addition, a flat surface of the touch panel without any positioning structure for the touching finger requires user's look and attention distracted away from a traveling direction of a vehicle, thereby deteriorating the operability of the touch panel.